Thanks, just for fun, have attached another pic
showing xoscope with siggen pet and same 1khz sine wave.

Yes I have continued interest in your idea to design a high frequency
s/w scope. Good luck with that.
All that stuff was right up my street while working as a test engineer
plus radio and broadcast engineer. (now retired)

From the suggested article "Frequency Multiplier For LF Measurements",
of course it's obvious that any s/w down-conversion would have to be external to the pc mic input socket, in order to be processed by the
sound card's natural bandwidth of only 20khz.

Skiing off-piste a bit to your efforts at recording Psicofonia on Baudline, yes I read what I could understand of the long Wikipedia article on this
subject - spooky and deep for me, but raises the point I was unaware that voices of the dead might be audible in the audio range.

All I hear at night is my wife snoring and the gentle roar of distant
traffic on the motorway near here, but no ghosts or spectres.
Perhaps you could enhance the chances of detecting "the other side",
by resting your laptop on a tomb in the local graveyard.
Beware though the voice from within, saying like actor Christopher Lee
"I am Dracula, I bid you welcome"

I will listen to the above interesting sound files and comment shortly.

First a serious tech contribution to complement the use
of xoscope, siggen and Baudline on a pc, laptop or netbook.
I have one of these always to hand on my test bench.

For those people who want a simple audio lab on their pc using
these and similar programs, I suggest including the attached mic
or line socket protection circuit to prevent accidental overload
of the sound card or motherboard sound module.

A sudden instantaneous high amplitude pulse signal will do
total expensive damage to these devices without protection,
so normal signal inputs should not exceed about 150mv RMS,
before top and bottom clipping occurs.

The Mic fader should be up about 1/3rd and Mic s/w boost must be off.

This is an easy safety project to construct on say veroboard
or tagboard, at very little component cost for big savings in
potential repair bills.

For those interested, the four diodes clamp the input
signal at top and bottom to about half a volt pk-pk.
The 470n capacitor blocks the phantom +3v dc coming OUT of the
mic socket, which would normally supply a fet microphone insert.

I listened to the sound files, if a bit short so couldn't
form an impression without being there, but a paranormal
expert might be interested.
-------------------------------------------------

Thanks for the added equalizer section but as you say,
better to keep the protection circuit simple.
The component values and configuration could
be useful though in another, different application.

Besides I want to discourage the lf response.
Lf should be rolled off downwards, don't like it.
Lf is a nuisance, having possibility of earth hum loop
disturbance and power supply breakthrough.
If anything it might be better to reduce the 470n to 100n
and also run the laptop from batteries.
Final cap value rests with the user, but 470n is a good start.

For the purpose of meaningful analyzer examination
of audio circuits, I think it better to concentrate
on frequencies above 1khz.

The small audio file belongs to a recording of may be 10 hours or so.
My recorder Sony is not very expensive, I think it cost me about 70 euros, but records clean sound. The voices are low and lose quality when I raise them by mhWaveEdit volume.

During the 10 hours nothing happens except in small moments that appear voices.

I have not devoted much time to this.

Anyway as I said this topic is out of this forum and the only thing interesting is that Puppy programs can also be useful for things like this.

----------------------------------------------------

With respect to the schema you're right, it is better to focus on frequencies above 1khz.

So your scheme is perfect.

If I have time and could get with some frequency converter circuit for xoscope and multiplier for siggen.

Quickly going back to your previous post,
IF I wanted to lift the lf end of the audio spectrum
I would just increase the value of a coupling cap
from a smaller value to about 10microfarads
to pass 20hz.
For this simple application, I wouldn't bother with
a bandpass filter at all.

The insertion loss of any such filter into its
termination Z would be self-defeating,
unless the facility exists to compensate by
amplification.
--------------------------------------------------------

Now, my last thought to complete a self-contained pc
set of audio lab analysis programs in Puppy, is an
absolute input audio level meter in millivolts of 10 to 100,

Although there are plenty of Windows programs
for this purpose which can run in Wine, could you
write a pet having an indicator and simple front panel
gui to calibrate against an external millivoltmeter?
Sorry, I'm a practical man knowing nothing of code,
it's way over my head.

No pressure just have a think, could it be done
at all. I will leave that with you.

Regarding the filters think your scheme is a good base, and then according to the needs of signal levels or frequency as may be modified according to the needs.

-----------------------------

Regarding millivoltmeter the only way that I have the do now:

| Microcontroller -- RS232| < == > | Program C | <==> | Gtkdialog|

At this time I managed to capture the data with the microcontroller and entirely by the program in C to pass gtkdialog program.

But I have problems with the C program that is not stable with the reception of data.

And this is the last thing I'm debugging.

But this way you would have to use microcontroller and maybe this will complicate your project.

Another way you could do serious thinking about it entirely by the sound card.

I have no experience in this, or how to aquire data from the sound card.

But as the sound card does not collect stable DC voltage values​​, you could mount a VCO, which CC values ​​changed frequency and using the card values ​​captured by presenting them as voltage values​​.

But as I say I have no experience in this.

Anyway when I finish my project I will put an example to capture data for microcontroller Puppy.

If the microcontroller predigests the data a little, you can script in Bash.

It seems to me that external electronics could also be made to precondition the analog signals so that a sound card could be used to get calibrated results. Sound cards use a delta-mod ADC so abrupt changes in the input to the ADC will cause the output to be bogus but if we assume that the edges get smoothed off, here is my idea:

We need a few controlling signals for the circuit so I will suggest a really bad way to get them:

Use a USB <--> RS232 adapter to make it so a script can send characters to the external circuit. In the external circuit, use a transistor to make RS232 levels into logic levels.

The character 7F or FF causes short pulses out of the transistor.
The character 20 or the like causes long pulses

A simple RC low pass from the logic level signal to the D of a 74HC74
A direct wire from the logic signal to the clock of the 74HC74

You now have a way to control an analog switch like a 74HC4053 to select between the calibration tone and the live signal.

So far we have only used 1 section of the 74HC74. The other two can be made into inverters by just having them select +5V and Ground for 0 and 5V in. One of those 5V's is the output of the 74HC74 for a reason I will explain below.

These inverters can by used to make a classic logic gate oscillator. If your 5V is in fact a reference and not a regulator, you will have nearly exactly 5Vp-p from the oscillator. A simple RC circuit can round it off AC couple and attenuate it.

The reason to make one of the inverter sections abnormal is so that when you select the live signal the oscillator is disabled. It has another advantage that is less obvious. When you select the calibration signal, the AC coupling will cause the base line of the rounded squarewave to slide from zero volts down to about half the peak to peak. A little clever code can look at this as a test of the low frequency behavor of the sound card.

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